1. Field of Invention
The present invention relates to a liquid crystal device. More particularly, the invention relates to a semi-transparent reflective liquid crystal display device.
2. Description of Related Art
Related art liquid crystal display devices can be broadly classified into three types, namely, a transparent type capable of image display in a transmission mode, a reflective type capable of image display in a reflection mode, and a semi-transparent reflective type capable of image display in both the transmission and reflection modes, and can be used as displays in notebook personal computers, televisions, and other devices because of their features, for example, thin style and light weight. In particular, semi-transparent reflective liquid crystal display devices can be used in various portable electronic apparatus because they adopt a combination of a transmission display mode and a reflection display mode, and can perform bright display with less power consumption even in a bright place or in a dark place by switching the display mode according to ambient brightness.
One type of such a semi-transparent reflective liquid crystal display device includes a liquid crystal display device in which a reflective layer made of a film of aluminum or the like, having slits (apertures) to transmit light, is provided on the surface of a lower substrate facing a liquid crystal layer to function as a semi-transparent reflective layer.
FIG. 11 shows an example of a semi-transparent reflective liquid crystal display device using this type of semi-transparent reflective layer.
In such a liquid crystal display device 100, a liquid crystal layer 103 is held between a pair of transparent substrates 101 and 102. A reflective layer 104 and an insulating film 106 are stacked on the lower substrate 101, and a lower electrode 108 made of a transparent conductive film of indium tin oxide (hereinafter “ITO”) or the like is formed thereon. An alignment film 107 is formed to cover the lower electrode 108. On the other hand, a color filter 109 having R (red), G (green) and B (blue) pigment layers is formed on the upper substrate 102, and a flattening film 111 is stacked thereon. Upper electrodes 112 made of a transparent conductive film of ITO or the like are formed on the flattening film 111, and an alignment film 113 is formed to cover the upper electrodes 112.
The reflective layer 104 is made of a metal film having a high reflectance, such as aluminum, and is provided with light-transmitting slits 110 corresponding to pixels. The slits 110 allow the reflective layer 104 to function as a semi-transparent reflective layer (hereinafter the layer is referred to as a “semi-transparent reflective layer”). A forward scattering plate 118, a phase difference film 119, and an upper polarizing plate 114 are arranged in that order on the outer surface of the upper substrate 102, and a phase difference film 115 and a lower polarizing plate 116 are arranged in that order on the outer surface of the lower substrate 101. A backlight 117 (an illumination device) is disposed under the lower surface of the lower substrate 101 and further under the lower polarizing plate 116.
In order to use the liquid crystal display device 100 shown in FIG. 11 in a bright place and in a reflection mode, external light, such as sunlight or illumination light, incidents from the upper side of the upper substrate 102, passes through the liquid crystal layer 103 and is reflected by the surface of the semi-transparent reflective layer 104 on the lower substrate 101, then passes again through the liquid crystal layer 103, and emits out of the upper side of the upper substrate 102. During the use in a dark place and in a transmission mode, light emitted from the backlight 117 disposed under the lower substrate 101 passes through the slits 110 of the semi-transparent reflective layer 104, passes through the liquid crystal layer 103, and emits out of the upper side of the upper substrate 102. Such light contributes to the display quality in each mode.
When the transmissive, reflective, and semi-transparent reflective liquid crystal display devices are viewed from the oblique direction, particularly in a transmission mode, problems regarding the viewing angle, for example, deterioration in display contrast, changes in display color, and tone reversal, are inevitable because of refractive index anisotropy of liquid crystal molecules. Therefore, it is advantageous to solve or address the above problems.
In related art transmissive liquid crystal display devices using a TN mode (twist angle of liquid crystal is 90°), as a method for addressing or solving the problems, the arrangement of optical compensation films between a liquid crystal cell and upper and lower polarizing plates can be manipulated.
One example is a structure in which optical compensation films having discotic liquid crystal aligned in hybrid alignment are disposed between a liquid crystal cell and upper and lower polarizing plates. Another example is a structure in which optical compensation films having liquid crystal polymers aligned in nematic hybrid alignment are disposed between a liquid crystal cell and upper and lower polarizing plates. This is disclosed in Japanese Patent Publication No. 2640083, Japanese Patent Laid-Open No. 11-194325, and Japanese Patent Laid-Open No. 11-194371.
In semi-transparent reflective liquid crystal display devices, it is necessary, on the principle of display, to provide circularly polarizing plates, each including one or more stretched films and a polarizing plate, on the upper side of a liquid crystal cell and between a semi-transparent reflective layer and a backlight in the transmission mode.
In order to increase the viewing angle in the transmission mode of the semi-transparent reflective liquid crystal display devices, a method using an optical compensation film of nematic hybrid alignment in the circularly polarizing plate disposed between the semi-transparent reflective layer and the backlight can be used. This is disclosed in Japanese Patent Laid-Open No. 2002-31717.